The invention relates generally to a system for processing sensor input and modifying output mapping and particularly, but not by way of limitation, to methods and apparatus for rate-adaptive pacing responsive to physiologic sensor input.
Many control systems rely on an output mapping to convert a measured control input to a desired control output. The output mapping is a graphical, tabular or other mathematical function of control output versus control input. As an example, a burner system with fuel and oxygen feeds may measure fuel feed rate as a control input and utilize output mapping to define the desired oxygen feed rate as a control output. The output mapping of oxygen feed rate versus fuel feed rate may not be linear, e.g., requiring increasing levels of excess oxygen at higher fuel feed rates to provide efficient burning of the fuel. Another example of control systems utilizing output mapping are some cardiac rhythm management systems.
Cardiac rhythm management systems include, among other things, pacemakers, also referred to as pacers. Pacemakers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via a transvenous leadwire having one or more electrodes disposed in the heart. Heart contractions are initiated in response to such pace pulses. By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its efficiency as a pump. Pacemakers are often used to treat patients with bradyarrhythmias, that is, hearts that beat too slowly, or irregularly.
There exists a class of pacemakers known as variable rate or rate-adaptive pacemakers which include a physiologic sensor indicative of metabolic demand and a variable rate pulse generator responsive to changes in metabolic demand. Some physiologic sensors for determining metabolic demand include minute ventilation (MV) sensors for measuring trans-thoracic impedance variations and generating an output signal varying as a function of the patient""s minute ventilation, and accelerometers for measuring body vibration during physical activity and generating an output signal varying as a function of the patient""s movement. Accelerometers are typically filtered and processed such that the resulting output signal is indicative of the patient""s exercising activity, and not of external vibration sources or internal noise. Other physiologic sensors are known in the art, e.g., blood pH, blood temperature, QT interval, blood oxygen saturation, respiratory rate and others.
Rate-adaptive pacemakers attempt to pace a patient""s heart at a rate corresponding to the patient""s metabolic demand. They accomplish this by utilizing an output mapping to convert a given sensor input to a unique output signal level. It is difficult to predict an appropriate pacing function capable of generating a paced rate corresponding to a patient""s metabolic demand at the time of implanting the pacemaker in the patient. To compensate for this deficiency, rate-adaptive pacemakers may incorporate logic to adjust the output mapping by comparing the patient""s average maximum sensor-indicated heart rate (AMSIR) to a sensor target rate (STR) at a prescribed or predetermined level of exercise activity. If the patient""s actual or demonstrated activity level differs from the predetermined activity level, the adjusting logic may inappropriately adjust the pacing function, resulting in a paced rate that is too high or too low for a given metabolic demand. If the paced rate is too high, the patient may feel palpitated or stressed. If too low, the patient may feel fatigued, tired or dizzy.
As will be seen from the above concerns, there exists a need for an improved method of adjusting output mapping in response to demonstrated sensor input. The above-mentioned problems with matching pacing to a patient""s metabolic demand and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
One embodiment includes a method of adjusting an output mapping of a control output versus a control input. The method includes obtaining signal input data and generating historical signal input data from the signal input data, wherein the historical signal input data is indicative of a breadth and/or frequency of the signal input data in excess of a reference value. The method further includes adjusting the output mapping in response to the historical signal input data. In another embodiment, the method includes increasing an area of the output mapping in response to increasing values of the breadth and/or frequency of the signal input data in excess of the reference value. In a further embodiment, obtaining signal input data includes obtaining data from the control input and/or from one or more auxiliary inputs.
A further embodiment includes a method of adjusting an output mapping of a control output versus a control input. The method includes obtaining signal input and generating historical signal input data. The method still further includes generating a first factor indicative of a breadth of the historical signal input data in excess of a reference value, generating a second factor indicative of a frequency of the historical signal input data in excess of the reference value, and adjusting the output mapping in response to the first and second factors. In a still further embodiment, adjusting the output mapping further includes increasing an area of the output mapping in response to increasing values of the first factor and decreasing the area of the output mapping in response to decreasing values of the first factor. In yet another embodiment, adjusting the output mapping further includes increasing an area of the output mapping in response to increasing values of the second factor and decreasing an area of the output mapping in response to decreasing values of the second factor. In a further embodiment, obtaining signal input data includes obtaining data from the control input and/or from one or more auxiliary inputs.
Yet another embodiment includes a method of adjusting a rate-adaptive curve for pacing a patient""s heart. The method includes sensing the patient""s activity, thereby producing sensed activity data, generating a demonstrated activity level from the sensed activity data, and adjusting the rate-adaptive curve in response to the demonstrated activity level relative to a predetermined activity level. In one embodiment, sensing the patient""s activity further includes receiving input from at least one physiologic sensor. In another embodiment, sensing the patient""s activity further includes receiving input from at least one physiologic sensor including minute ventilation sensors and/or accelerometers. In a further embodiment, adjusting the rate-adaptive curve further includes increasing the rate-adaptive curve when the demonstrated activity level exceeds the predetermined activity level and decreasing the rate-adaptive curve when the demonstrated activity level is less than the predetermined activity level. In a still further embodiment, the predetermined activity level corresponds to a prescribed exercise level and frequency.
One embodiment includes a method of adjusting a rate-adaptive curve for pacing a patient""s heart. The method includes sensing the patient""s activity having an exertion level, generating a factor indicative of a breadth of the patient""s exertion levels above a predetermined exertion level, and adjusting at least a portion of the rate-adaptive curve in response to the factor. In another embodiment, the factor increases for increasing breadth of the patient""s exertion levels above the predetermined exertion level.
Another embodiment includes a method of adjusting a rate-adaptive curve for pacing a patient""s heart. The method includes sensing the patient""s activity having an exertion time at an exertion level, generating a factor indicative of a frequency of the patient""s exertion levels above a predetermined exertion level, and adjusting at least a portion of the rate-adaptive curve in response to the factor. In another embodiment, the factor increases for increasing frequency of the patient""s exertion levels above the predetermined exertion level.
A further embodiment includes a method of adjusting a rate-adaptive curve for pacing a patient""s heart. The method includes sensing the patient""s activity having both an exertion level, and an exertion time at the exertion level. The method further includes generating a first factor indicative of a breadth of the patient""s exertion levels above a predetermined exertion level, generating a second factor indicative of the patient""s exertion time at exertion levels above the predetermined exertion level, and adjusting at least a portion of the rate-adaptive curve in response to the first and second factors. In one embodiment, the first factor increases for increasing breadth of the patient""s exertion levels above the predetermined exertion level. In another embodiment, the second factor increases for increasing frequency of the patient""s exertion levels above the predetermined exertion level.
A still further embodiment includes a control system. The control system includes a processor, a memory coupled to the processor and having first data stored thereon defining an output mapping, a regulator coupled to the processor, a control input coupled to the processor, and a control output coupled to the regulator. The processor is adapted to sample second data from the control input, store the sampled second data to the memory, thereby generating historical signal input data, and adjust the output mapping in response to the historical signal input data.
Yet another embodiment includes a control system. The control system includes a processor, a memory coupled to the processor, a regulator coupled to the processor, a control input coupled to the processor, at least one auxiliary input coupled to the processor, and a control output coupled to the regulator. The memory has instructions stored thereon capable of causing the processor to perform a method including storing first data to the memory defining an output mapping, sampling second data from the control input, storing the sampled second data to the memory, thereby generating historical control input data, sampling third data from the at least one auxiliary input, and storing the sampled third data to the memory, thereby generating historical auxiliary input data. The method further includes generating a first factor indicative of a breadth of the historical control input data above a first reference value and a breadth of the historical auxiliary input data above a second reference value. The method still further includes generating a second factor indicative of a frequency of the historical control input data above the first reference value and a frequency of the historical auxiliary input data above the second reference value. The method still further includes increasing the output mapping in response to increasing values of the first factor and decreasing the output mapping in response to decreasing values of the first factor, and increasing the output mapping in response to increasing values of the second factor and decreasing the output mapping in response to decreasing values of the second factor.
One embodiment includes a rate-adaptive pacemaker. The rate-adaptive pacemaker includes a processor, a memory coupled to the processor, a variable-rate pulse generator coupled to the processor, and at least one physiologic sensor input coupled to the processor. The memory has instructions stored thereon capable of causing the processor to perform a method including storing first data to the memory defining a rate-adaptive curve, sampling second data from the at least one physiologic sensor input indicative of a patient""s activity, storing the sampled second data to the memory, thereby generating historical activity data, and adjusting the first data defining the rate-adaptive curve in response to the historical activity data.
Another embodiment includes a rate-adaptive pacemaker. The rate-adaptive pacemaker includes a processor, a memory coupled to the processor, a variable-rate pulse generator coupled to the processor, and at least one physiologic sensor input coupled to the processor. The memory has instructions stored thereon capable of causing the processor to perform a method including storing first data to the memory defining a rate-adaptive curve, and sampling second data from the at least one physiologic sensor input indicative of a patient""s activity having an exertion level and an exertion time at the exertion level. The method further includes storing the sampled second data to the memory, thereby generating historical activity data. The method still further includes generating a first factor indicative of a breadth of the patient""s exertion levels above a predetermined exertion level, generating a second factor indicative of the patient""s exertion time at exertion levels above the predetermined exertion level, and adjusting at least a portion of the rate-adaptive curve in response to the first and second factors.
The invention further includes other apparatus and methods of varying scope.